Ion-exchange membrane having an imprinted non-woven substrate

ABSTRACT

The present disclosure provides an ion-exchange membrane that includes a supporting substrate impregnated with an ion-exchange material. The supporting substrate includes an imprinted non-woven layer, and the imprinting includes a plurality of deformations at a surface density of at least 16 per cm 2 . The supporting substrate may lack a reinforcing layer. In some examples, the supporting substrate may include only a single layer of the imprinted non-woven fabric.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage Entry of International ApplicationNo. PCT/US2017/023214, filed Mar. 20, 2017.

FIELD

The present disclosure relates to ion-exchange membranes with anon-woven layer.

BACKGROUND

The following paragraphs are not an admission that anything discussed inthem is prior art or part of the knowledge of persons skilled in theart.

Ion-exchange membranes are used as electrolytic membranes forelectrodialysis (ED), bipolar ED, reversed electrodialysis (RED),electrodeionization (EDI), and electrodialysis reversal (EDR). Thesepurification processes transport ions from one solution to anothersolution through the ion-exchange membrane under the influence of anapplied electric potential difference.

Ion-exchange membranes useful for electrodialysis include anion-exchange material and a supporting substrate for the ion-exchangematerial. In ion-exchange membranes produced using a woven or non-wovenfabric sheet as the supporting substrate, voids in the woven ornon-woven fabric sheet are filled with the ion-exchange material.

INTRODUCTION

The following introduction is intended to introduce the reader to thisspecification but not to define any invention. One or more inventionsmay reside in a combination or sub-combination of the apparatus elementsor method steps described below or in other parts of this document. Theinventors do not waive or disclaim their rights to any invention orinventions disclosed in this specification merely by not describing suchother invention or inventions in the claims.

Using non-woven fabric in ion-exchange membranes is desirable as thehighly interlaced structure of fibers in non-woven fabric may reduceleaking, electrical resistance, thickness, or any combination thereof,in comparison to membranes formed using woven fabrics. However, amembrane formed only using non-woven fabric often has an undesirablephysical property when compared to membranes formed using woven fabrics.The undesirable physical property may be reduced strength, reduceddimensional stability, or reduced shape stability. For example; amembrane formed with a single layer of non-woven substrate may curl oncuring of the ion-exchange polymer at an elevated temperature.

In order to improve at least one of the undesirable physical properties,ion-exchange membranes made with non-woven fabrics may include areinforcing layer. However, the addition of a reinforcing layerincreases the thickness of the membrane and, as a result, the resistanceof the membrane also increases.

Reducing the thickness of an ion-exchange membrane is desirable as suchreduction may result in higher throughput from an electrolytic cellstack; all other conditions being equal, since more membranes may beloaded into the same device. Reducing the thickness of the ion-exchangemembranes may result in a reduction of chemicals consumed for a givenarea of membrane since thinner membranes have less ion-exchange materialper surface area of membrane. Reducing the thickness of the ion-exchangemembranes may result in a reduction of energy consumption in anelectrolytic purification process if it corresponds with a reduction inresistance of the thinner membranes.

Ion-exchange membranes having a reinforcing layer attached to anon-woven fabric layer may also expand irregularly when in saltsolutions, which results in undulation of the membranes. The irregularexpansion is due to the differences in expansion, or contraction, of thetwo layers when in the salt solution.

Therefore, there remains a need for an ion-exchange membrane with anon-woven layer that addresses or ameliorates one or more shortcomingsassociated with an ion-exchange membrane formed from a single layer ofnon-woven fabric, or with an ion-exchange membrane formed from anon-woven fabric and a reinforcing layer.

In some examples, the present disclosure provides an ion-exchangemembrane having a supporting substrate impregnated with an ion-exchangematerial. The supporting substrate includes an imprinted non-wovenlayer, where the imprinting includes a plurality of deformations at asurface density of at least 16 per cm². The imprinting may be debossing;embossing, or a combination thereof.

In some examples, the present disclosure provides a method of making anion-exchange membrane. The method includes saturating or impregnating asupporting substrate with a solution that includes an anionic orcationic monomer and a crosslinker; and polymerizing the monomer andcrosslinker at an elevated temperature. The supporting substrateincludes an imprinted non-woven layer, where the imprinting includes aplurality of deformations at a surface density of at least 16 per cm².The imprinting may be debossing, embossing, or a combination thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure will now be described, by way ofexample only, with reference to the attached Figures.

FIG. 1 is an illustration of an exemplary debossed non-woven layerhaving depressions into the surface of the fabric.

FIG. 2 is an illustration of an exemplary debossed non-woven layerhaving depressions into the surface of the fabric and reciprocaldepressions in the opposite surface of the fabric.

FIG. 3 is an illustration of an exemplary embossed non-woven layerhaving protrusions from the surface of the fabric and correspondingdepressions in the opposite surface of the fabric.

FIG. 4 is an illustration of an exemplary embossed non-woven layerhaving protrusions from both surfaces of the fabric.

FIG. 5 is a flow chart illustration a method according to the presentdisclosure.

DETAILED DESCRIPTION

Generally, the present disclosure provides an ion-exchange membrane thatincludes a supporting substrate impregnated with an ion-exchangematerial. The supporting substrate includes an imprinted non-wovenlayer, and the imprinting includes a plurality of deformations at asurface density of at least 16 per cm². The imprinting may be debossing,embossing, or a combination thereof. In some examples, the imprintednon-woven fabric may have physical properties that allow the supportingsubstrate to exclude a reinforcing layer. In some examples, theimprinted non-woven fabric may have physical properties that allow thesupporting substrate to include only a single layer of the imprintednon-woven fabric.

Ion-exchange membranes formed with such an imprinted non-woven layer mayhave improved dimensional stability or shape stability during membranecuring at elevated temperature in comparison to membranes that areotherwise identical but lack the impriting. For example, an ion-exchangemembrane according to the present disclosure may be smoother, flatterand/or have fewer wrinkles than an otherwise identical ion-exchangemembrane that has a deformation-free non-woven layer. Without wishing tobe bound by theory, the authors of the present disclosure believe thatthe deformations in the non-woven layer inhibit or terminate thedevelopment of distortions in Iong fibres of the non-woven layer, inparticular when the non-woven layer is impregnated or saturated with theion-exchange components and cured at an elevated temperature.

In the context of the present disclosure, “debossing” refers toimprinting a design into a material and leaving a depressed imprint ofthe design in the surface of the material. The depressed imprint is alsoreferred to as the “debossed” imprint. A layer of fabric that has beensubjected to a debossing step may be referred to as a “debossed fabric”.The expression “embossing” refers to imprinting a design into a materialand leaving a raised imprint of the design in the material. The raisedimprint is also referred to as the “embossed” imprint. A layer of fabricthat has been subjected to an embossing step may be referred to as an“embossed fabric”.

The imprinted non-woven layer may have at least 30, at least 50, or atleast 100 deformations per cm². The imprinted non-woven layer may haveno more than 200 deformations per cm². It should be understood that thepresent disclosure contemplates all imprinted non-woven layers havingfrom 16 to 200 deformations per cm², and contemplates all possibleranges encompassed by 16 to 200 deformations per cm².

The deformations in the non-woven layer may make up from about 10% toabout 90% of the surface area of the imprinted non-woven layer. This maybe calculated by viewing the non-woven layer from above, measuring thetotal visible area of the deformations, and dividing by the totalsurface area. For example, in a square centimeter of non-woven fabrichaving 16 deformations that are each 2×2 mm square, the deformationswould make up 64% of the surface area.

In some examples, the deformations in the imprinted non-woven layer maybe depressions in the surface of the fabric, as illustrated in FIG. 1,which illustrates a cross-section of a debossed fabric. Fabric (10)includes deformations that are depressions (12) in the surface of thefabric (14). In this exemplary fabric, the thickness of the debossednon-woven layer is illustrated as (T), the depth of the depressions (12)is illustrated as (D). The surface area of the exemplary depressions maybe calculated at least partially based on dimension W. For example, ifthe depressions (12) are square-shaped, then the area of a deformationwould be W².

In other examples, the deformations in the imprinted non-woven layer maybe depressions in the surface of the fabric with reciprocal depressionsin the opposite surface of the fabric, as illustrated in FIG. 2. Fabric(20) includes deformations that are depressions (22) in the surface ofthe fabric (24). The depressions (22) have reciprocal depressions (26)in the opposite surface of the fabric (28). In this exemplary fabric,the thickness of the debossed non-woven layer is illustrated as (T), thedepth of the depressions (22) is illustrated as (0), and the depth ofthe opposite depressions (26) is illustrated as (DI The surface area ofthe exemplary depressions may be calculated at least partially based ondimension W. As illustrated in FIG. 2, depth “D” is not identical todepth “a”. That is, the depth of the reciprocal depressions into theopposite surfaces do not need to be identical. A debossed non-wovenlayer according to the present disclosure, but not illustrated in thefigures, may include depressions in opposite surfaces of the fabric,though the depressions do not have reciprocal depressions in theopposite surface.

Using a fabric as illustrated in FIG. 1 or 2 as a support in anion-exchange membrane would result in ion-exchange polymer both (a) inthe debossed depressions, and (b) impregnated in voids of the fibers ofthe non-woven fabric.

The debossed non-woven layer may be from about 50 μm to about 700 μmthick. Using a debossed non-woven layer having a thickness from about100 μm to about 300 μm may provide a beneficial balance betweenelectrical resistance, mechanical strength, and shape stability. Thedeformations may have an average total depth, as measured from anon-debossed portion of the surface of the non-woven layer, that is5-99% of the thickness of the debossed non-woven layer. In particularexamples, the average total depth may be from 40-60% of the thickness ofthe debossed non-woven layer. In the context of the debossingillustrated in FIG. 1, this corresponds to depth “D” being from 5% to99% of the thickness “T”. In the context of the debossing illustrated inFIG. 2, this corresponds to the total of depth “0” plus depth “D′” beingfrom 5% to 99% of the thickness “T”.

For example, the debossed non-woven layer may be 50 μm thick, and havedepressions into only one surface of the non-woven layer, where thedepressions have an average depth of 25 μm, corresponding to 50% of thethickness of the debossed non-woven layer. In another example, thedebossed non-woven layer may have depressions into both surfaces of thenon-woven layer, where the depression have an average depth of 50 μmfrom one surface and 25 μm from the opposite surface. If the debossednon-woven layer is 100 μm thick the depressions represent 75% of thetotal thickness of the layer.

In still other examples, the deformations in the imprinted non-wovenlayer may be protrusions from only one surface of the fabric withcorresponding depressions in the opposite surface of the embossedfabric, as illustrated in FIG. 3. Fabric (30) includes deformations (32)that are protrusions (34) from the surface of the fabric (36). Theprotrusions (34) have corresponding depressions (38) in the oppositesurface of the fabric (40). In this exemplary fabric, the totalthickness of the embossed non-woven layer is illustrated as (T) and theheight of the protrusions is illustrated as (H). The surface area of theexemplary protrusions may be calculated at least partially based ondimension W.

An exemplary imprinted non-woven layer having protrusions on bothsurfaces is illustrated in FIG. 4. Fabric (50) includes deformations(52) that are protrusions (54) on both surfaces of the fabric. Theprotrusions (54) have corresponding depressions (56) in the oppositesurfaces.

Using a fabric as illustrated in FIG. 3 or 4 as a support in anion-exchange membrane would result in ion-exchange polymer (a) in thedepressions opposite the embossed protrusions, and (b) impregnated invoids of the fibers of the non-woven fabric. In some examples, such asfabrics having closely spaced embossed deformations, the ion-exchangepolymer may also be in the space between the protrusions. It would bebeneficial for the ion-exchange polymer to be in the space between theprotrusions because the corresponding ion-exchange membrane would have asmoother surface. An ion-exchange membrane having ion-exchange polymeronly in the depressions opposite the embossed protrusions andimpregnated in voids of the fibers may be more easily damaged becausethe protrusions would be brittle and not protected by any surroundingion-exchange polymer.

The embossed non-woven layer may be from about 50 μm to about 1000 μmthick, including the height of the deformations. Using an embossednon-woven layer having a total thickness from about 100 μm to about 300μm may provide a beneficial balance between electrical resistance,mechanical strength, and shape stability. The deformations may have anaverage height, as measured from a non-embossed portion of the surfaceof the non-woven layer, that is 5-99% of the total thickness of theembossed non-woven layer.

In particular examples, the average height of the embossed protrusionsmay be from 40-60% of the total thickness of the embossed non-wovenlayer. For example, the embossed non-woven layer may be 50 μm thick (nottaking the height of the protrusions into account), and have protrusionson only one surface of the layer (such as illustrated in FIG. 3), wherethe protrusions have an average height of 50 μm. The total thickness ofsuch an embossed non-woven layer is 100 μm since the total thickness isdetermined by taking the height of the protrusions into account. In sucha non-woven layer, the protrusions represent 50% of the thickness of thelayer. In another example, the embossed non-woven layer may haveprotrusions on both surfaces of the layer (such as illustrated in FIG.4), where the protrusions have an average height of 50 μm on one surfaceand 25 μm on the opposite surface. If the embossed non-woven layer is 50μm thick when not taking the height of the protrusions into account, thetotal thickness of the embossed non-woven layer is 125 μm since thetotal height takes the heights of the protrusions on both surfaces intoaccount. In such a layer, the protrusions represent 60% of the totalthickness of the layer.

If the density of a non-woven layer does not change, the unit weight ofthe non-woven layer increases as the thickness of the non-woven layer(not taking the height of any embossed protrusions into account)increases. However, two different non-woven layers may have differentdensities, in which case the unit weights may be different for the samethickness. The unit weight of the non-woven layer may be from about 10g/m² to about 260 g/m².

The debossed deformations may include depressions into a single surfaceof the non-woven layer (as illustrated in FIG. 1), or depressions intoopposite surfaces of the non-woven layer (as illustrated in FIG. 2). Innon-woven layers having depressions into opposite surfaces of thenon-woven layer, (a) the debossed non-woven layer may have substantiallyequal numbers of depressions per cm² on each side of the oppositesurfaces, (b) the depressions may make up substantially the same amountof surface area on each side of the opposite surfaces, (c) thedepressions into the opposite surfaces of the debossed non-woven layermay be of substantially the same depth, (d) the depressions into theopposite surfaces of the debossed non-woven layer may be ofsubstantially the same size, (e) the depressions into the oppositesurfaces of the debossed non-woven layer may be of substantially thesame shape, or (f) any combination thereof.

The embossed deformations may include protrusions from a single surfaceof the embossed non-woven layer (as illustrated in FIG. 3), orprotrusions from opposite surfaces of the embossed non-woven layer (asillustrated in FIG. 4). In non-woven layers having protrusions onopposite surfaces of the non-woven layer, (a) the embossed non-wovenlayer may have substantially equal numbers of protrusions per cm² oneach side of the opposite surfaces, (b) the deformations may make upsubstantially the same amount of surface area on each side of theopposite surfaces, (c) the protrusions on the opposite surfaces of theembossed non-woven layer may be of substantially the same height, (d)the protrusions on the opposite surfaces of the embossed non-woven layermay be of substantially the same size, (e) the protrusions on theopposite surfaces of the embossed non-woven layer may be ofsubstantially the same shape, or (f) any combination thereof.

Ion-exchange membranes made with a non-woven layer that has deformationson both sides (as illustrated in FIGS. 2 and 4) may have improved shapestability during membrane curing, such as by reducing curling, incomparison to membranes made with a non-woven layer having deformationsinto only one side (as illustrated in FIGS. 1 and 3). Shape stabilitymay be further improved when (a) the depths or heights of thedeformations are substantially the same on both sides of the non-wovenlayer, (b) the total surface areas of the deformations are substantiallythe same on both sides of the non-woven layer, or (c) both. Withoutwishing to be bound by theory, the authors of the present disclosurebelieve that the more similar the two sides of the non-woven layer, theless prone the membrane will be to curling during membrane curing.

In the context of the present disclosure, two sets of deformationsshould be considered to be of substantially the same depth, be ofsubstantially the same height, be of substantially the size, or coversubstantially the same surface area if the values are within 10% of theaverage of the two values. For example, two sets of depressions shouldbe considered to be of substantially the same depth if the depressionsin one area of a non-woven layer (such as on one side of the substrate)have an average depth of 110 μm and the depressions in another area ofthe non-woven layer (such as on the opposite side of the substrate) havean average depth of 90 μm. In this example, the depth of 90 μm and 110μm fall within ±10% of the 100 μm average. In another example, two setsof depressions into opposite sides of the substrate should be consideredto cover substantially the same surface area if the depressions on oneside cover 45% of the area and the depressions on the other side cover55% of the area. In this example, the values of 45% and 55% are bothwithin ±10% of the 50% average.

The deformations in the non-woven layer may have a shape that is:circular, triangular, square-shaped, rectangular, diamond-shaped,star-shaped, oval, or any combination thereof. It is desirable for thedeformations to be uniformly distributed across the non-woven layer.“Uniformly distributed” should be understood to mean that the number ofdeformations in every given square centimeter of the non-woven layershould be within ±10% of the average number of deformations per squarecentimeter over the whole layer. For example, if the non-woven layer has100 deformations/cm², then every square centimeter must have from 90 to110 deformations in order for the deformations to be considered“uniformly distributed”. In some examples of uniformly distributeddeformations, the deformations are regularly spaced apart, for examplein rows and columns, or in diagonal arrangements.

The non-woven layer may be a non-woven fabric sheet of: polyester,polypropylene, polyethylene, polyamide, polyacrylonitrile, or polyvinylchloride. Polyester is acid stable and may be used to make a membranefor EDR, such as a membrane that includes a polymer formed from apolymerization that includes: (a) N-trimethylaminoethylmethacrylatechloride (TMAEMC) and ethylene glycol dimethacrylate (EGDM); (b)dimethylaminopropyl methacrylamide (DMAPMA), cyclohexanedimethanoldiglycidyl ether (CHDMDGE), HCl and N-vinyl caprolactam (V-Cap); (c)vinyl benzyl chloride (VBC), divinylbenzene (DVB), tributyl amine (TBA),and dibutyl amine (DBA); or (d) 2-acrylamido-2-methylpropane sulfonicacid (AMPS) and EGDM. Polypropylene is base stable and maybe be used tomake a membrane for ED, such as a membrane that includes a polymerformed from a polymerization that includes: (a) lithium styrenesulfonate (LiSS) and divinyl benzene (DVB), (b)(vinylbenzyl)trimethylammonium chloride (VBTAC) and DVB; or (c) vinylbenzyl chloride (VBC), divinylbenzene (DVB), tributyl amine (TBA), anddibutyl amine (DBA).

The ion-exchange material may be a cation-exchange polymer havingsulfonic acid groups, carboxylic acid groups, phosphoric acid groups, orsalts thereof. For example, the cation-exchange polymer may be a polymerformed from the polymerization with 2-acrylamido-2-methylpropanesulfonic acid, sodium 2-acrylamido-2-methylpropane sulfonate, potassium3-sulfopropyl acrylate, sodium methallyl sulfonate, sodium vinylsulfonate, sodium 4-vinylbenzenesulfonate, lithium4-vinylbenzenesulfonate, acrylic acid, 2-ethylacrylic acid, methacrylicacid, 2-propylacrylic acid, sodium acrylate, sodium methacrylate,ethylene glycol methacrylate phosphate, vinylphosphonic acid, orbis[2-(methacryloyloxy)ethyl] phosphate.

Alternatively, the ion-exchange material may be an anion-exchangepolymer having quaternary ammonium groups, imidazolium groups,pyridinium groups, or salts thereof. For example, the anion-exchangepolymer may be a polymer formed from the polymerization withN-trimethylaminoethylmethacrylate chloride (TMAEMC),[2-(acryloyloxy)ethyl] trimethylammonium chloride,[2-(methacryloyloxy)ethyl] trimethylammonium chloride,(3-acrylamidopropyl) trimethylammonium chloride,[3-(methacryloylamino)propyl]trimethylammonium chloride,diallyldimethylammonium chloride, (vinylbenzyl)trimethylammoniumchloride, 1-vinyl-3-ethylimidazolium bromide, or 4-vinylpyridiniumtribromide.

The cation- and anion-exchange polymers preferably also includecross-linkers since cross-linkers increase the strength and dimensionstability of the resulting polymer. A suitable cross-linker is selectedbased on the polymerization chemistry required by the monomer. Examplesof cross-linkers that may be used to form membranes of the presentdisclosure include: N,N′-methylenebis(acrylamide),N,N′-(1,2-dihydroxyethylene)bisacrylamide, N,N′-ethylenebis(acrylamide),hexamethylenebis(methacrylamide), poly(ethylene glycol) diacrylamide,piperazine diacrylamide, 1,3-butanediol diacrylate, neopentyl glycoldiacrylate, di(ethylene glycol) diacrylate, 1,3-butanedioldimethacrylate, tetra(ethylene glycol) diacrylate, tri(ethyleneglycol)diacrylate, glycerol 1,3-diglycerolate diacrylate, poly(propyleneglycol) diacrylate, 1,4-butanediol diacrylate, and the cross-linkersmentioned above with respect to the exemplary polyester andpolypropylene fabrics.

The ion-exchange membrane may be impregnated with ion-exchange materialhaving an ion exchange capacity (IEC) of at least 1.6 meq/g of dryion-exchange material. It should be understood that is the IEC iscalculated without taking into account the weight of the substrate.

An ion-exchange membrane according to the present disclosure may be usedin an electrolytic cell stack. Such an electrolytic cell stack couldinclude a plurality of the ion-exchange membranes.

The present disclosure also provides a method of making an ion-exchangemembrane. The method is illustrated in FIG. 5. The method (110) includessaturating or impregnating (112) a supporting substrate (114) having animprinted non-woven layer, as discussed above, with a reaction solution(116) that includes an anionic or cationic monomer and a crosslinker.The imprinting includes a plurality of deformations at a surface densityof at least 16 per cm². The imprinting may be embossing, debossing, or acombination thereof. The supporting substrate may lack a reinforcinglayer. In some examples, the supporting substrate may include only asingle layer of the imprinted non-woven fabric.

The monomer and crosslinker are polymerized (118) to form theion-exchange membrane (120), such as at an elevated temperature or underUV initiated radical polymerization. For example, the saturated orimpregnated supporting substrate may be heated at a temperature that isincreased from room temperature to as high as 130° C. This increase intemperature may be effected by passing the saturated or impregnatedsupporting substrate over one or more heating tables that provideheating zones of increased temperatures. The heating table or tables maydefine a heating zone of about 20 meters long.

The anionic or cationic monomer and the crosslinker may be dissolved ina solvent, along with a radical initiator, to form the reactionsolution. A skilled person would understand that a suitable solvent isone that dissolves the reagents, is unreactive under polymerizationconditions, and that may be removed from the resulting membrane.Examples of suitable solvents are discussed in the examples below. Theradical initiator may be a thermal initiator or a UV initiator,depending on the desired conditions for polymerization. Examples ofsuitable initiators are discussed in the examples below. Additionalexemplary initiators are discussed in EP 3 040 365 and incorporatedherein by reference.

Examples

Non-woven polyester fabrics. Seven different non-woven polyester fabricswere used to make either anion- or cation-exchange membranes. Theanion-exchange membranes were made from the polymerization ofN-trimethylaminoethylmethacrylate chloride (16.3 g) and ethylene glycoldimethacrylate (15.5 g) in the presence of dimethyl2,2′-azobis(2-methylpropionate) (V-601, 0.22 g), a radical initiator.The reagents were dissolved in 18 g of dipropylene glycol (DPG). Thiscombination of monomer and crosslinker is referred to as “AR204”.

The cation-exchange membranes were made from the polymerization of 21.8g of 2-acrylamido-2-methylpropane sulfonic acid and 26.2 g of ethyleneglycol dimethacrylate in the presence of 0.8 g of V-601 (which is apolymerization initiator) and 0.005 g of mono methyl ether ofhydroquinone (MeHQ) (which is a polymerization inhibitor for acrylic andacrylamide monomers). The reagents were dissolved in a solution of 2.7 gof water and 29.3 g of 1-methyl-2-pyrollidinone (NMP). This combinationof monomer and crosslinker is referred to as “CR67”.

The seven polyester fabrics, all from Toray, had the followingproperties:

TABLE 1 Tensile Unit Total strength Air Sample Deformation Deformationsweight thickness (N/5cm) permeability No. shape per cm² (g/m²) (μm) MDCD (cc/s/cm²) #1 circle  32  (4 × 8) 28 180 120  30 200 #2 circle  32 (4 × 8) 43 200 210  95 120 #3 square 100 (10 × 10) 70 180 370 180  29#4 diamond  32  (4 × 8) 40 160 165  85 175 #5 diamond  32  (4 × 8) 55220 240 130 100 #6 diamond  32  (4 × 8) 70 240 300 170  80 #7 circle  32 (4 × 8) 70 340 200  55  50

The polyester fabrics had debossed imprints whose depths were at least40% of the total thickness. The fabric in the debossed imprints wasnearly transparent.

Cation- and anion-exchange membranes made with Sample 3 were found to beacceptably smooth and acceptably flat, with no spalling on the surface.

The following tables show various properties associated with cation- andanion-exchange membranes made with Sample 3 using four different batchesof the cation- and anion-exchange polymers. The cation- andanion-exchange membranes are referred to as “CR67-PE” and “AR204-PE”,respectively.

TABLE 2 Water Water Perm- IEC Content Transport selectivity Sample(meq/g) (%) (ml/F) (%) AR204-PE Batch 1 1.95 41.4 133.75 90.3 AR204-PEBatch 2 1.91 41.1 127 89.01 AR204-PE Batch 3 1.835 43.08 146 92.26AR204-PE Batch 4 1.88 43.04 147.5 91.81 Average 1.89 42.16 138.6 90.8

TABLE 3 Water Water Perm- IEC Content Transport selectivity Sample(meq/g) (%) ( ml/F) (%) CR67-PE Batch 1 1.84 44.7 196.5 87.1 CR67-PEBatch 2 2.1 46.4 201 87.3 CR67-PE Batch 3 2.41 51.16 214 88.39 CR67-PEBatch 4 1.92 44.14 197 88.49 Average 2.07 46.6 202.1 87.8

TABLE 4 Resistance (Ω · cm²) Thick- in 0.1N in 0.5N in 1N ness SampleNaCl NaCl NaCl (μm) AR204-PE Batch 1  3.2 ± 0.08 2.19 ± 0.05 1.42 ± 0.07~170 AR204-PE Batch 2  3.4 ± 0.36 2.24 ± 0.09 1.84 ± 0.18 ~200 AR204-PEBatch 3 4.19 ± 0.74 2.51 ± 0.28 2.07 ± 0.23 ~190 AR204-PE Batch 4 3.88 ±0.60 2.41 ± 0.03 1.76 ± 0.14 ~170 Average 3.67 2.34 1.77 182

TABLE 5 Resistance (Ω · cm²) Thickness Sample in 0.1N NaCl in 0.5N NaClin 1N NaCl (μm) CR67-PE Batch 1 3.80 ± 0.20 3.26 ± 0.09 2.85 ± 0.16 ~170CR67-PE Batch 2 4.36 ± 0.81 2.73 ± 0.26 2.99 ± 0.63 ~160 CR67-PE Batch 34.56 ± 0.85 2.18 ± 0.45 2.18 ± 0.33 ~160 CR67-PE Batch 4 5.18 ± 0.803.56 ± 0.26 2.52 ± 0.43 ~170 Average 4.48 2.94 2.64 165

Ion exchange capacity (IEC) was measured by titration. Water content wascalculated by [(wet weight−dry weight)/(wet weight−backingweight)]×100%. Water transport was determined by measuring the watervolume that passed through the membrane when 1 Faraday of charge wasapplied. Permselectivity was obtained by measuring the electricpotential across the membrane when a gradient of NaCl solution of 1 Nover 0.5 N is used. The resistances of the membranes in a NaCl solutionswere measured using a non-contact resistance measurement device. Thethicknesses of the membranes were determined using a spiral micrometer.

Non-woven polypropylene fabrics. Two different non-woven polypropylenefabrics were used to make either anion- or cation-exchange membranes.The fabrics were from Toray. The anion-exchange membranes were made fromthe polymerization of 28.9 g of (vinylbenzyl) trimethylammonium chloride(VBTAC) and 29.7 g of divinyl benzene (DVB) in the presence of 0.9 mL oftertbutylperoxy-2-ethylhexyl carbonate (TPO), a radical initiator. Thereagents were dissolved in 38.5 of dipropylene glycol (DPG). Thiscombination of monomer and crosslinker is referred to as “AR103”.

The cation-exchange membranes were made from the polymerization of 17.6g lithium styrene sulfonate (LiSS) and 15.2 g of divinyl benzene in thepresence of 0.2 g of V-601. The reagents were dissolved in 24.0 g of1-methyl-2-pyrollidinone (NMP). This combination of monomer andcrosslinker is referred to as “CR61”.

The two polypropylene fabrics, both from Toray, had the followingproperties:

TABLE 6 Tensile Unit Total strength Sample Deformation Deformationsweight thickness (N/5cm) No. shape per cm² (g/m²) (μm) MD CD #1 oval 64(8 × 8) 50 370 120 75 #2 square 36 (6 × 6) 60 410 145 95

The polypropylene fabrics had debossed imprints whose depths were atleast 40% of the total thickness. The fabric in the debossed imprintswas nearly transparent.

The following tables show various properties associated with cation- andanion-exchange membranes made with the two polypropylene fabrics usingtwo different batches of the cation- and anion-exchange polymers. Thecation- and anion-exchange membranes are referred to as “CR61-PP” and“AR103-PP”, respectively.

TABLE 7 Water Water Perm- IEC Content Transport selectivity Sample(meq/g) (%) (ml/F) (%) AR103-PP Batch 1 2.10 36 115 92 AR103-PP Batch 22.15 35 110 93 Average 2.13 35.5 112.5 92.5

TABLE 8 Water Water Perm- IEC Content Transport selectivity Sample(meq/g) (%) (ml/F) (%) CR61-PP Batch 1 2.22 44 160 90 CR61-PP Batch 22.30 46 150 91 Average 2.26 45 155 90.5

TABLE 9 Resistance (Ω · cm²) Thickness Sample in 0.1N NaCl in 0.5N NaClin 1N NaCl (μm) AR103-PP Batch 1 7.52 ± 0.28 4.66 ± 0.32 3.18 ± 0.27~400 AR103-PP Batch 2 8.13 ± 0.55 5.22 ± 0.18 3.56 ± 0.33 ~450 Average7.83 4.94 3.37 450

TABLE 10 Resistance (Ω · cm²) Thickness Sample in 0.1N NaCl in 0.5N NaClin 1N NaCl (μm) CR61-PP Batch 1 7.28 ± 0.38 4.36 ± 0.51 3.01 ± 0.18 ~400CR61-PP Batch 2 7.95 ± 0.23 5.68 ± 0.36 3.25 ± 0.58 ~500 Average 7.624.72 3.13 450

Ion exchange capacity (IEC), water content, water transport,permselectivity, resistance, and thickness were measured as discussedabove.

In the preceding description, any discussion of a range of values shouldbe understood to disclose all possible individual values within therange and all possible ranges falling with the range. For example, adiscussion of from about 1 to about 100″ should be understood to be adisclosure of every individual value from about 1 to about 100 (forexample 2, 10.7, 50, 80.5, and 92) and every range that falls in therange of about 1 to about 100 (for example 10-20, 5-95, 75-80.5, and24.3-47.5).

In the preceding description, for purposes of explanation, numerousdetails are set forth in order to provide a thorough understanding ofthe examples. However, it will be apparent to one skilled in the artthat these specific details are not required. Accordingly, what has beendescribed is merely illustrative of the application of the describedexamples and numerous modifications and variations are possible in lightof the above teachings.

Since the above description provides exemplary examples, it will beappreciated that modifications and variations can be effected to theparticular examples by those of skill in the art. Accordingly, the scopeof the claims should not be limited by the particular examples set forthherein, but should be construed in a manner consistent with thespecification as a whole.

What is claimed is:
 1. An ion-exchange membrane comprising: a supportingsubstrate impregnated with an ion-exchange material, wherein thesupporting substrate comprises an imprinted non-woven layer before beingimpregnated with the ion exchange material, the imprinted non-wovenlayer comprising a plurality of imprinted deformations at a surfacedensity of at least 16 per cm².
 2. The ion-exchange membrane accordingto claim 1, wherein the imprinted non-woven layer comprises at least 30imprinted deformations per cm².
 3. The ion-exchange membrane accordingto claim 1, wherein the non-woven layer comprises no more than 200imprinted deformations per cm².
 4. The ion-exchange membrane accordingto claim 1, wherein the supporting substrate lacks a reinforcing layer.5. The ion-exchange membrane according to claim 1, wherein thesupporting substrate consists essentially of a single layer of theimprinted non-woven layer.
 6. The ion-exchange membrane according toclaim 1 wherein the imprinted deformations make up from about 10% toabout 90% of the surface area of the imprinted non-woven layer.
 7. Theion-exchange membrane according to claim 1, wherein the imprintednon-woven layer is a debossed non-woven layer comprising debosseddeformations.
 8. The ion-exchange membrane according to claim 7, whereinthe debossed non-woven layer has a thickness from about 50 μm to about700 μm.
 9. The ion-exchange membrane according to claim 7, wherein thedebossed deformations have an average depth, as measured from anon-debossed portion of the surface of the non-woven layer, that is5-99% of the thickness of the debossed non-woven layer.
 10. Theion-exchange membrane according to claim 9, wherein the debosseddeformations have an average depth that is 30-70% of the thickness ofthe debossed non-woven layer.
 11. The ion-exchange membrane according toclaim 7, wherein the debossed deformations comprise depressions into asingle surface of the debossed non-woven layer, or depressions intoopposite surfaces of the debossed non-woven layer.
 12. The ion-exchangemembrane according to claim 11, wherein the debossed deformationscomprise depressions into opposite surfaces of the debossed non-wovenlayer and wherein a) the debossed non-woven layer has substantiallyequal numbers of depressions per cm² on each side of the oppositesurfaces, (b) the depressions make up substantially the same amount ofsurface area on each side of the opposite surfaces, (c) the depressionsinto the opposite surfaces of the debossed non-woven layer are ofsubstantially the same depth, (d) the depressions into the oppositesurfaces of the debossed non-woven layer are of substantially the samesize, (e) the depressions into the opposite surfaces of the debossednon-woven layer are of substantially the same shape, or (f) anycombination thereof.
 13. The ion-exchange membrane according to claim 1,wherein the imprinted non-woven layer is an embossed non-woven layercomprising embossed deformations.
 14. The ion-exchange membraneaccording to claim 13, wherein the embossed non-woven layer has a totalthickness of from about 50 μm to about 1,000 μm.
 15. The ion-exchangemembrane according to claim 13, wherein the embossed deformations havean average height, as measured from a non-embossed portion of thesurface of the non-woven layer, that is 5-99% of the total thickness ofthe embossed non-woven layer.
 16. The ion-exchange membrane according toclaim 15, wherein the embossed deformations have an average height thatis 30-70% of the total thickness of the embossed non-woven layer. 17.The ion-exchange membrane according to claim 13, wherein the embosseddeformations comprise protrusions from a single surface of the embossednon-woven layer, or protrusions from opposite surfaces of the embossednon-woven layer.
 18. The ion-exchange membrane according to claim 17,wherein the embossed deformations comprise protrusions from oppositesurfaces of the embossed non-woven layer and wherein a) the embossednon-woven layer has substantially equal numbers of protrusions per cm²on each side of the opposite surfaces, (b) the protrusions make upsubstantially the same amount of surface area on each side of theopposite surfaces, (c) the protrusions from the opposite surfaces of theembossed non-woven layer are of substantially the same height, (d) theprotrusions from the opposite surfaces of the embossed non-woven layerare of substantially the same size, (e) the protrusions from theopposite surfaces of the embossed non-woven layer are of substantiallythe same shape, or (f) any combination thereof.
 19. The ion-exchangemembrane according to claim 1, wherein the supporting substrate has aunit weight of from about 10 g/m² to about 260 g/m².
 20. Theion-exchange membrane according to claim 1, wherein the deformationsare: circular, triangular, square-shaped, rectangular, diamond-shaped,star-shaped, oval, or any combination thereof.
 21. The ion-exchangemembrane according to claim 1, wherein the supporting substrate is anon-woven fabric sheet of: polyester, polypropylene, polyethylene,polyamide, polyacrylonitrile, or polyvinyl chloride.
 22. Theion-exchange membrane according to claim 1, wherein the ion-exchangematerial is a cation-exchange polymer having sulfonic acid groups,carboxylic acid groups, phosphoric acid groups, or salts thereof. 23.The ion-exchange membrane according to claim 22, wherein thecation-exchange polymer is a polymer formed from the polymerization ofone or more monomers selected from the group consisting of2-acrylamido-2-methylpropane sulfonic acid, sodium2-acrylamido-2-methylpropane sulfonate, potassium 3-sulfopropylacrylate, sodium methallyl sulfonate, sodium vinyl sulfonate, sodium4-vinylbenzenesulfonate, lithium 4-vinylbenzenesulfonate, acrylic acid,2-ethylacrylic acid, methacrylic acid, 2-propylacrylic acid, sodiumacrylate, sodium methacrylate, ethylene glycol methacrylate phosphate,vinylphosphonic acid, and bis[2-(methacryloyloxy)ethyl] phosphate. 24.The ion-exchange membrane according to claim 1, wherein the ion-exchangematerial is an anion-exchange polymer having quaternary ammonium groups,imidazolium groups, or pyridinium groups.
 25. The ion-exchange membraneaccording to claim 24, wherein the anion-exchange polymer is a polymerformed from the polymerization of one or more monomers selected from thegroup consisting of N-trimethylaminoethylmethacrylate chloride (TMAEMC),[2-(acryloyloxy)ethyl] trimethylammonium chloride,[2-(methacryloyloxy)ethyl] trimethylammonium chloride,(3-acrylamidopropyl) trimethylammonium chloride,[3-(methacryloylamino)propyl] trimethylammonium chloride,diallyldimethylammonium chloride, (vinylbenzyl)trimethylammoniumchloride, 1-vinyl-3-ethylimidazolium bromide, and 4-vinylpyridiniumtribromide.
 26. The ion-exchange membrane according to claim 1, whereinthe ion-exchange membrane is impregnated with ion-exchange materialhaving an ion exchange capacity of at least 1.6 meq/g of dryion-exchange material.
 27. An electrolytic cell stack comprising aplurality of ion-exchange membranes according to claim
 1. 28. Theion-exchange membrane according to claim 1, wherein the supportingsubstrate consists of a single layer of the imprinted non-woven layer.29. The ion-exchange membrane according to claim 1 wherein the ionexchange material substantially fills one or more of (i) the imprinteddeformations and (ii) spaces between the imprinted deformations.